The invention set forth in this specification pertains to new and improved magnetic recording members such as are commonly utilized in conjunction with computers of various known types as memory discs or the like.
Such recording members are conventionally constructed utilizing a disc shaped substrate of a metal such as aluminum or brass appearing somewhat like a common phonograph record. The surface of such a substrate is commonly coated with a magnetic recording alloy layer and such a layer in turn is normally covered with a protective covering of one sort or another. In general effective magnetic recording alloys as are used in such magnetic recording layers will normally contain from about 50 to about 97% by weight cobalt and from about 3 to about 50% by weight nickel and, if other secondary ingredients are present in such alloys, from about 3 to 50% by weight such secondary ingredients. A particularly suitable magnetic recording alloy contains about 70% by weight cobalt, about 5% by weight phosphorous and about 25% by weight nickel.
Such magnetic recording alloy layers can be from about 3 to about 100 microinches thick, although generally they are from about 14 to about 20 microinches thick. The precise composition of such a layer and the precise thickness of such a layer will depend upon an intended use of a magnetic recording member. As such members are used they are employed in connection with a transducer in such a manner that there is relative rotation between the transducer and the recording member.
In order to avoid damage to the recording alloy layer in a magnetic recording member a number of different expedients have been proposed and adopted to varying extents. It is not considered that an understanding of the present invention requires a detail discussion of all of such expedients. However, a brief review of certain of these prior ways of protecting the surface of a magnetic recording alloy layer is considered helpful in understanding the need for the present invention.
Thin films of wax, wax-like or other organic compositions have been utilized as protective coverings over such an alloy layer. Such films have only limited physical resistance against abrasion and the like. They will tend to accumulate upon the head of a transducer utilized with a magnetic recording member. Because of this it is not considered desirable to protect a magnetic recording alloy layer in this manner. It is frequently considered that effective protection of a magnetic alloy layer can be achieved by forming on the surface of an alloy layer an oxide coating from the material in the alloy layer itself.
This type of expedient has been considered to be especially desirable because of the physical properties of cobalt oxide. Inasmuch as magnetic recording alloys as indicated in the preceding predominantly contain cobalt, an oxide coating produced from such alloys will predominantly contain cobalt oxides. It is usually considered that most satisfactory coatings consist primarily of cobalt oxidized to the form of the combined oxide Co.sub.3 O.sub.4. This oxide is non-magnetic and, hence, will not interfere with the intended use of a magnetic recording alloy. Further, it is physically comparatively strong when formed by a conventional process such as oxidation of cobalt in air or oxygen. Also it has a coefficient of friction which makes it desirable for use where there is relative movement between a transducer and a magnetic recording member.
The invention set forth in this specification grows out of a recognition that cobalt oxide protective coverings formed upon a magnetic recording member by methods such as air oxidation or oxidation in oxygen of the surface of a magnetic recording alloy are somewhat disadvantageous. In general even when chemical expedients such as the use of carefully controlled solutions are employed to prepare such magnetic recording alloy layers for oxidation the protective coverings tend to be of a nonuniform character. When this occurs there is, of course, a corresponding nonuniformity in the magnetic recording alloy layer supporting such a protective oxide layer.
In considering the importance of this it must be realized that the recording members to which this invention relates are used primarily in computer work. Even small variations in a magnetic recording alloy layer are quite critical from an operative standpoint in connection with such uses. Further, it must be realized that the alloy layers are employed in such recording members are comparatively thin. This has the effect of tending to accentuate even comparatively small imperfections or variations in such layers.